Twenty-four patients with Acanthamoeba keratitis have been
reported to CDC from 14 states in the last 9 months (Table 1).
Although onset of illness for some patients dates to as early as
1982,
most had onset of illness in 1985 or 1986. In two patients, the
infected eye was enucleated; 12 patients underwent corneal
transplantation.

Twenty (83%) of the patients wore contact lenses. Of these,
two
wore hard lenses (one hard, the other rigid gas-permeable); four
wore
extended-wear soft lenses; and 14 wore daily-wear soft lenses. Ten
of
these 20 patients cleaned their lenses with home-made saline
solution
prepared by mixing salt tablets with bottled, distilled, nonsterile
water; four used commercially available lens-cleaning solutions
followed by a tap water rinse; one used commercial bottled saline;
and
one cleaned lenses with tap water pumped from a private well. No
lens-care information was available for four patients.

Editorial Note

Editorial Note: Members of the genus Acanthamoeba are the most
common
free-living amoebae in fresh water and soil. They have been
isolated
from brackish and sea water, airborne dust, and hot tubs.
Acanthamoebae have also been recovered from the nose and throat of
humans with impaired respiratory function and from apparently
healthy
persons, suggesting that these organisms are commonly inhaled (1).
It
is, therefore, not surprising that acanthamoebae may contaminate
contact lenses or lens-cleaning/soaking fluids.

The first case of Acanthamoeba keratitis in the United States
was
reported in 1973 in a South Texas rancher with a history of trauma
to
his right eye (1). A. polyphaga was repeatedly cultured from his
cornea, and both trophozoite and cyst forms of the organism were
demonstrated in the corneal sections. Since then, 31 patients have
been diagnosed in the United States (excluding those reported
here).
Nineteen of these 31 cases have been published (2-12); seven
occurred
before 1981; four occurred in 1981; one, in 1982; five, in 1983;
and
two, in 1984. The 24 Acanthamoeba keratitis cases described here
represent a striking increase over those reported in previous
years.
A similar increase has been observed in the use of contact lenses
during the past 5 years, from 14.5 million in 1980 to 23.1 million
in
1985 (13).

Review of the 19 published cases indicates that nearly all
infections were preceded by some degree of ocular trauma and/or
exposure to contaminated water. Only recently has it been
suggested
that wearing contact lenses or using contaminated
lens-cleaning/soaking solution may predipose the wearer to
developing
Acanthamoeba keratitis (10). Although information on contact lens
use
was not specified in all the published reports, at least 13 of the
19
patients were known users, and in the present report, 20 (83%) of
24
patients wore contact lenses.

Acanthamoebae are resistant to killing by freezing,
dessication, a
variety of antimicrobial agents, and levels of chlorine that are
routinely used to disinfect municipal drinking water, swimming
pools,
and hot tubs (14). Recent studies indicate that thermal
disinfection
systems for contact lenses are superior to cold chemical
disinfection
in preventing the growth of Acanthamoeba (15). Although 10 of the
20
patients who wore contact lenses used home-made saline cleaning
solutions, it is not known how many of them heat-sterilized the
solutions before use.

Since the clinical characteristics of Acanthamoeba keratitis,
especially the irregular epithelial lesions, the stromal
infiltrative
keratitis, and edema seen in most patients may resemble HSV
keratitis,
many patients are initially diagnosed and treated for this
infection.
Until recently, the correct diagnosis was made only after detailed
histologic examination of corneal tissue removed at the time of
transplantation. The following clinical features are suggestive of
Acanthamoeba keratitis: (1) severe ocular pain; (2) a
characteristic
360-degree or partial paracentral stromal ring infiltrate; (3)
recurrent corneal epithelial breakdown; and (4) a corneal lesion
refractory to the usual medications. The diagnosis can be
confirmed
by vigorously scraping the cornea with a swab or platinum-tipped
spatula, staining the material obtained with Giemsa or trichrome
stain, and examining it at 400X with a standard light microscope.
In
addition, some of the corneal scrapings should be cultured on
non-nutrient agar seeded with Escherichia coli (1).

Medical management of Acanthamoeba keratitis is complicated by
the
resistance of these organisms to most of the commonly used
antibacterial, antifungal, antiprotozoal, and antiviral agents.
Although some patients have recently been treated successfully
using
ketoconazole, miconazole, and propamidine isethionate (Brolene*),
penetrating keratoplasty usually has been necessary to recover
useful
vision (5,7-11). Further studies are needed to better estimate the
true risk of infection, to improve diagnostic and treatment
methods,
and to evaluate the ability of different lens cleaning/soaking
solutions to prevent growth of Acanthamoeba.

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